1. Field of the Invention
The present invention relates generally to an apparatus and mobile communication system for transmitting data streams in a wireless communication system, and in particular, to an apparatus and method for transmitting data streams in a wireless communication system with multiple antennas.
2. Description of the Related Art
In general, a mobile communication system is one of the typical wireless communication systems. The mobile communication system has been originally developed to support voice communication. Recently, however, there is an increasing demand for high-speed data communication as well as the voice transmission. To meet the demand, many attempts to efficiently transmit data streams are being made in the mobile communication system. As a result, the mobile communication system is evolving into a high-speed, high-quality wireless packet data communication system to provide a data service and a multimedia service as well as the existing voice service. The standardization efforts for High Speed Downlink Packet Access (HSDPA) led by 3rd Generation Partnership Project (3GPP) and 1× Evolution Data and Voice (EV-DV) led by 3rd Generation Partnership Project 2 (3GPP2) are being made to find a solution for providing a high-speed, high-quality wireless packet data service at 2 Mbps or higher in the 3rd generation (3G) mobile communication system. The future 4th generation (4G) mobile communication system aims at providing a high-speed, high-quality multimedia service at a rate higher than 2 Mbps.
As one of the attempts to transmit packet data at high speed, a multi-antenna technique has been proposed. The multi-antenna technique can be roughly classified into two techniques: a beamforming technique (also known as a smart antenna technique) and an antenna diversity technique. The former detects a position of a mobile station and forms a beam in the detected direction in the process of transmitting transmission signals through antenna beams. The latter obtains diversity gain by providing array antennas to a transmitter and a receiver.
When the array antennas are used, the transmission efficiency mainly depends on the number of transmission data streams and modulation schemes therefor. Therefore, the next generation wireless communication system, in which the array antennas are used, requires an apparatus and method for effectively determining the number of data streams that can be transmitted through each antenna, and a modulation scheme used for transmission of the data streams through the corresponding antenna.